Deck 12: The Three-Phase, Squirrel-Cage Induction Motor

Question 1

In a three-phase AC induction motor, a typical ____________________ contains a three-phase winding mounted in the slots of a laminated steel core.

Answer 1

stator

Question 2

What is the formula for synchronous speed?

Answer 2

Synchronous speed is determined by the following formula: RPM = (120 x f) / p.
RPM = Synchronous speed
f = Hertz (frequency)
p = Number of stator poles per phase

Question 3

What are the main components of the three-phase AC induction motor?

Answer 3

The three-phase AC induction motor normally consists of a stator, a rotor, and two end shields housing the bearings that support the rotor shaft.

Question 4

If a squirrel-cage induction motor is loaded beyond the breakdown torque, there will be a corresponding decrease in torque until the point is reached where the motor stalls.

Question 5

The ____________________ is the revolving part of the motor and consists of steel punchings or laminations arranged in a cylindrical core.

Question 6

A(n) ____________________ provides information vital to the proper selection and installation of the motor.

Question 7

Briefly explain why the power factor of a squirrel-cage induction motor at no load is low.

Question 8

The speed performance of a squirrel-cage induction motor is measured in terms of ____________________.

Question 9

Manufacturers' guarantees for standard motor ratings are usually based on operation at any altitude up to 3,300 ft.

Question 10

In reference to a squirrel-cage induction motor, as the value of percent slip decreases toward 0%, the speed performance of the motor decreases.

Question 11

In addition to information provided on the motor nameplate, what additional reference would allow the electrician to determine the conduit, wire, and starting and running protection sizes needed?

Question 12

When a three-phase AC induction motor is connected across the full line voltage, the starting surge of current is approximately the same as the rated full-load current.

Question 13

Both the delta-connected and star-connected patterns for three-phase motors involve nine leads. In the event that the lead markings are destroyed, how can an electrician determine whether the motor is delta connected or star connected?

Question 14

The ____________________ motor is relatively small in physical size for a given horsepower rating when compared with other types of motors and, due to its rugged construction and reliable operation, this motor is widely used for many industrial applications.

Question 15

The squirrel-cage induction motor has very poor speed regulation characteristics.